I can't vouch for this story, but here is what I've heard:
John Jacob Niles said that while he was sitting in some bistro in Marseilles, he heard a group of Barbados sailors (what Barbados sailors were doing in Marseilles, I'm not sure) singing Venezuela, and he learned it from them. Some years later, Burl Ives recorded the song, but apparently didn't properly credit Niles. Niles sued him for breach of copyright and won! Ives said, "I thought you said you learned it from a bunch of sailors." Niles responded, "I lied! I wrote it!"
When Richard Dyer-Bennet sang a concert in Seattle a few decades ago, he alluded to this incident and told the audience that, true or not, he is always very careful to give proper credit to John Jacob Niles before he sings the song.
Niles claimed to have written a large number of songs that everybody assumes are traditional, including Black is the Color of My True Love's Hair, despite the fact that there is ample evidence that most of these songs were kicking around in one form or another long before Niles chose to grace our planet with his presence. Good songs. Interesting singer. Strange Man. He gave a whole new dimension to the expression "credibility gap."